1. Field of the Invention
The present invention relates to a cathode-ray tube apparatus used in a TV receiver, a computer display, and the like, and in particular, to a cathode-ray tube apparatus provided with a velocity modulation coil.
2. Description of the Related Art
As one method for realizing higher image quality in a TV receiver, for example, there is the enhancement of an edge of an image. In order to enhance an edge of an image, a velocity modulation coil is provided in a cathode-ray tube apparatus. The velocity modulation coil is provided at a neck of a cathode-ray tube or in the vicinity thereof, and generates a magnetic field in a vertical direction to modulate the horizontal scanning velocity of an electron beam, thereby enhancing an edge of an image (e.g., see JP 57(1982)-45650 U).
In the color cathode-ray tube apparatus, the increase in a diameter of an electron beam spot on a phosphor screen ascribed to the recent enlargement of a screen, the increase in an anode voltage for higher brightness, and the enhancement in flatness of a front panel are proceeding. Along with these, there is a demand for a further higher intensity in a magnetic field for enhancing an edge of an image.
Under the above-mentioned circumstances, a color cathode-ray tube apparatus has been proposed that is capable of increasing the intensity of a magnetic field acting on an electron beam without increasing a current that flows through a velocity modulation coil and without increasing the winding number of the velocity modulation coil (e.g., see JP 6(1994)-283113 A).
In the color cathode-ray tube apparatus described in JP 6(1994)-283113 A, magnetic substances are placed in upper and lower portions of respective electron beam passage apertures for three electron beams (R, G, B) provided in a fifth grid (G5 electrode) of an electron gun housed in a neck, and a velocity modulation coil is placed at a position on an outer circumference of the neck corresponding to the G5 electrode.
According to the above configuration, a magnetic flux generated in the velocity modulation coil is focused by the magnetic substances, and the magnetic flux can be concentrated in an electron beam passage region, whereby the intensity of a magnetic field contributing to the velocity modulation of electron beams can be increased.
However, due to the loss caused by an eddy current generated on the surface of the electrode (G5 electrode) that is a metal component, the intensity of a magnetic field generated in the electron beam passage region in the G5 electrode is inherently low. Thus, even if such a magnetic field with a low intensity is increased by the magnetic substances, the effect thereof cannot be expected sufficiently. That is, in the color cathode-ray tube apparatus of JP 6(1994)-283113 A, the sensitivity of velocity modulation (velocity modulation amount of an electron beam with respect to an input current to the velocity modulation coil) is not so enhanced as expected. Furthermore, the magnetic substances and the G5 electrode are welded to each other, so that the number of processes for welding such small components to each other is large, which increases the production cost.
Furthermore, a deflection magnetic field generated by a horizontal deflection coil and a vertical deflection coil for allowing electron beams emitted from the electron gun to scan the phosphor screen is distributed to the electron gun side on which the velocity modulation coil is provided. Thus, it is desired to prevent the distribution of the deflection magnetic field from being influenced to cause deflection distortion by enhancing the sensitivity of velocity modulation.